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<title>Layer Bands using a Background Part</title>
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          <h1 class="mb-0 p-1 ">GoJS</h1>
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    <!-- Start of GoJS sample code -->
    
    <script src="../release/go.js"></script>
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    <script id="code">

    // this controls whether the layout is horizontal and the layer bands are vertical, or vice-versa:
    var HORIZONTAL = true;  // this constant parameter can only be set here, not dynamically

    // Perform a TreeLayout where commitLayers is overridden to modify the background Part whose key is "_BANDS".
    function BandedTreeLayout() {
      go.TreeLayout.call(this);
      this.layerStyle = go.TreeLayout.LayerUniform;  // needed for straight layers
    }
    go.Diagram.inherit(BandedTreeLayout, go.TreeLayout);

    BandedTreeLayout.prototype.commitLayers = function(layerRects, offset) {
      // update the background object holding the visual "bands"
      var bands = this.diagram.findPartForKey("_BANDS");
      if (bands) {
        var model = this.diagram.model;
        bands.location = this.arrangementOrigin.copy().add(offset);

        // make each band visible or not, depending on whether there is a layer for it
        for (var it = bands.elements; it.next();) {
          var idx = it.key;
          var elt = it.value;  // the item panel representing a band
          elt.visible = idx < layerRects.length;
        }

        // set the bounds of each band via data binding of the "bounds" property
        var arr = bands.data.itemArray;
        for (var i = 0; i < layerRects.length; i++) {
          var itemdata = arr[i];
          if (itemdata) {
            model.setDataProperty(itemdata, "bounds", layerRects[i]);
          }
        }
      }
    };
    // end BandedTreeLayout


    function init() {
      var $ = go.GraphObject.make;

      myDiagram = $(go.Diagram, "myDiagramDiv",
        {
          layout: $(BandedTreeLayout,  // custom layout is defined above
            {
              angle: HORIZONTAL ? 0 : 90,
              arrangement: HORIZONTAL ? go.TreeLayout.ArrangementVertical : go.TreeLayout.ArrangementHorizontal
            }),
          "undoManager.isEnabled": true
        });

      myDiagram.nodeTemplate =
        $(go.Node, go.Panel.Auto,
          $(go.Shape, "Rectangle",
            { fill: "white" }),
          $(go.TextBlock, { margin: 5 },
            new go.Binding("text", "key")));

      // There should be at most a single object of this category.
      // This Part will be modified by BandedTreeLayout.commitLayers to display visual "bands"
      // where each "layer" is a layer of the tree.
      // This template is parameterized at load time by the HORIZONTAL parameter.
      // You also have the option of showing rectangles for the layer bands or
      // of showing separator lines between the layers, but not both at the same time,
      // by commenting in/out the indicated code.
      myDiagram.nodeTemplateMap.add("Bands",
        $(go.Part, "Position",
          new go.Binding("itemArray"),
          {
            isLayoutPositioned: false,  // but still in document bounds
            locationSpot: new go.Spot(0, 0, HORIZONTAL ? 0 : 16, HORIZONTAL ? 16 : 0),  // account for header height
            layerName: "Background",
            pickable: false,
            selectable: false,
            itemTemplate:
              $(go.Panel, HORIZONTAL ? "Vertical" : "Horizontal",
                new go.Binding("position", "bounds", function(b) { return b.position; }),
                $(go.TextBlock,
                  {
                    angle: HORIZONTAL ? 0 : 270,
                    textAlign: "center",
                    wrap: go.TextBlock.None,
                    font: "bold 11pt sans-serif",
                    background: $(go.Brush, "Linear", { 0: "aqua", 1: go.Brush.darken("aqua") })
                  },
                  new go.Binding("text"),
                  // always bind "width" because the angle does the rotation
                  new go.Binding("width", "bounds", function(r) { return HORIZONTAL ? r.width : r.height; })
                ),
                // option 1: rectangular bands:
                $(go.Shape,
                  { stroke: null, strokeWidth: 0 },
                  new go.Binding("desiredSize", "bounds", function(r) { return r.size; }),
                  new go.Binding("fill", "itemIndex", function(i) { return i % 2 == 0 ? "whitesmoke" : go.Brush.darken("whitesmoke"); }).ofObject())
                // option 2: separator lines:
                //(HORIZONTAL
                //  ? $(go.Shape, "LineV",
                //      { stroke: "gray", alignment: go.Spot.TopLeft, width: 1 },
                //      new go.Binding("height", "bounds", function(r) { return r.height; }),
                //      new go.Binding("visible", "itemIndex", function(i) { return i > 0; }).ofObject())
                //  : $(go.Shape, "LineH",
                //      { stroke: "gray", alignment: go.Spot.TopLeft, height: 1 },
                //      new go.Binding("width", "bounds", function(r) { return r.width; }),
                //      new go.Binding("visible", "itemIndex", function(i) { return i > 0; }).ofObject())
                //)
              )
          }
        ));

      myDiagram.linkTemplate =
        $(go.Link,
          $(go.Shape));  // simple black line, no arrowhead needed

      // define the tree node data
      var nodearray = [
        { // this is the information needed for the headers of the bands
          key: "_BANDS",
          category: "Bands",
          itemArray: [
            { text: "Zero" },
            { text: "One" },
            { text: "Two" },
            { text: "Three" },
            { text: "Four" },
            { text: "Five" }
          ]
        },
        // these are the regular nodes in the TreeModel
        { key: "root" },
        { key: "oneB", parent: "root" },
        { key: "twoA", parent: "oneB" },
        { key: "twoC", parent: "root" },
        { key: "threeC", parent: "twoC" },
        { key: "threeD", parent: "twoC" },
        { key: "fourB", parent: "threeD" },
        { key: "fourC", parent: "twoC" },
        { key: "fourD", parent: "fourB" },
        { key: "twoD", parent: "root" }
      ];

      myDiagram.model = new go.TreeModel(nodearray);
    }
    window.addEventListener('DOMContentLoaded', init);
  </script>

<div id="sample">
  <div id="myDiagramDiv" style="border: solid 1px black; width:100%; height:600px;"></div>
  <p>
    Unlike swim lane diagrams where the nodes are supposed to stay in their lanes,
    layer bands run perpendicular to the growth direction of the layout.
  </p>
  <p>
    This sample uses a custom <a>TreeLayout</a> that overrides the <a>TreeLayout.commitLayers</a> method
    in order to specify the position and size of each "band" that surrounds a layer of the tree.
    The "bands" are held in a single Part that is bound to a particular node data object whose key is "_BANDS".
    The headers, and potentially any other information that you might want to display in the headers,
    are stored in this "_BANDS" object in an Array.
  </p>
  <p>
    This sample can be adapted to use a <a>GraphLinksModel</a> instead of a <a>TreeModel</a>
    and a <a>LayeredDigraphLayout</a> instead of a <a>TreeLayout</a>.
  </p>
</div>
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